The goal of Core D Is to provide the leadership, administrative oversight as well as statistical analysis and related quality control to insure the completion of the specific aims of Projects 1 through 4, as well as the successful continuance of the Nurses' Health Study cohort. The specific aims are as follows: 1. To provide overall leadership to the Program Project and the Nurses' Health Study. 2. To provide administrative oversight for the Program Project. 3. To provide statistical expertise and programming support to insure the completion of Project 1-4 aims. 4. To maintain and further develop quality control measures related to data analysis and documentation. 5. To support and facilitate use of Nurses' Health Study resources by collaborating scientists. In Core D, we provide the structure and resources to facilitate continued communication between all Cores and Projects, as well as all investigators working with the cohort. The Core coordinates the regular bi-weekly meeting of NHS investigators as well as the annual meeting of the External Advisory Committee. All Program Project-related IRB activities are conducted through this core. We also provide a framework for data analyses as well as specific biostatistical support for Projects 1-4; computer programming is provided under the direction of study biostatisticians and project investigators. In addition, the Core provides an ongoing program of quality control and data documentation that are necessary to help insure that all users of the NHS data base are knowledgeable and aware of both its strengths and limitations, and publications are accurate and error free. Finally, by providing support for all initial queries from potential collaborators as well as data documentation, the Core facilitates the use of the Nurses' Health Study research platform for a range of scientific collaborations.